Pretreatment of beryllium prior to coating



Patented Mar. 11 1952 PRETREATMEN T OF BERYLLIUM PRIOR TO COATING Morris Kolodney, New York, N. Y., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application May 14, 1948,

Serial No. 27,151

This invention relates to methods for treating a metal so that it may be more effectively coated, and more specifically, to methods for treating beryllium so that it may be covered with a smooth, uniformly adherent coating.

Pure beryllium has a gray-white luster when it is freshly machined, but it readily tarnishes. This is also true of metal compositions containing a major proportion by weight of beryllium. It is necessary to maintain an inert atmosphere or cover the beryllium metal compositions in order to protect them from oxidation. It is also sometimes necessary to coat beryllium with a smooth, pore-tight coating of various metals for use in scientific experiments. However, priorto the time of this invention no method was known for producing a smooth, uniformly adherent coating even on clean, freshly machined beryllium metal compositions.

It is, therefore, the primary object of this invention to provide a quick and eflicient method for treating beryllium metal objects, and beryllium alloys or beryllium compacts containing a major proportion by weight of beryllium, so that they may subsequently be covered with a smooth, uniformly adherent coating.

It is a further object of this invention to enable the uniform coating of beryllium metal compositions containing small amounts of other alloying elements.

It is a still further object of this invention to provide compositions of matter with which to treat beryllium or beryllium objects so that the objects may be unformly coated.

Still further objects and advantages of this invention will be apparent from the following description.

The objects of this invention are achieved by the process of etching the beryllium by making it anodic in an electrolyte comprising a mixture of a strong polybasic inorganic oxygen-containing acid and a strong monobasic oxygen-free acid. The electrolyte used in the etching step is advantageously a mixture of an aqueous solution of orthophosphoric acid and hydrochloric acid. The etch may be if desired further improved by immersing the beryllium object in a solution containing sulfate ions. After the beryllium is etched, it may be coated by a number of different methods. It is usually desirable first to clean the beryllium thoroughly before it is etched.

The following example gives a presently preferred embodiment of the invention for the pur- 2 Claims. (01. 20432) 2 pose of illustrating it, but not for the purpose of limiting its spirit and scope.

Example I A beryllium object about 2 inches by 2 inches current density is adjusted to 0.5 ampere per square inch, and is maintained at this value for three minutes. The beryllium block is then Washed in water.

After the preliminary. cleaning step the beryllium object is placed in a beaker containing 100 cubic centimeters of concentrated per cent) orthophosphoric acid, cubic centimeters of water and 2 cubic centimeters of hydrochloric acid. The solution thereby consists essentially of about 49 percent by volume of concentrated phosphoric acid, about 49 percent by volume of water and about 0.9 percent by volume of hydrochloric acid. The beryllium is connected to an anode lead and a block of nickel is connected to a cathode lead. Potential is applied and the current density is adjusted to 0.5 ampere per square inch, and maintained at this value for 5 minutes. After the current is turned 01f the beryllium is washed inwater. It is then dipped in an aqueous solution containing 20 grams of ammonium sulfate and 10 cubic centimeters of concentrated sulfuric acid in 200 cubic centimeters of water.

The cleaned beryllium object is placed in a container which is then sealed and evacuated, The beryllium is heated to 300 C. by means of an external high-frequency induction heating coil in order to further clean and outgas it. The temperature is then adjusted at 200 C., the evacuation is discontinued, and nickel carbonyl is admitted at a pressure of 15 centimeters. The pressure rises as the nickel deposits and carbon monoxide is formed. When the pressure reaches the proper value in the previously calibrated system, the gas is' pumped out. The finished piece is cooled with the aid of helium, and finally re-, moved from the vacuum system. a

The beryllium object coated in this manner is covered with a smooth, uniformly adherent porefree coating.

Many modifications of themethod of the in:

A 1 inch diameter, 0.5 inch high beryllium metal compact cylinder containing 95 per cent beryllium is cleaned and degreased by immersion in acetone. The beryllium metal composition and a carbon electrode of about the same size are connected to anode and cathode leads respectively and are then immersed in a stainless steel dish containing 50 cubic centimeters of 85 per cent orthophosphoric acid, 150 cubic centimeters of water and 2 cubic centimeters of concentrated hydrofluoric acid. Potential is applied, and the current density is adjusted to 0.3 ampere per square inch and maintained at this value for from 5 to 10. minutes. The bath is operated at room temperature. In about minutes the surface of the beryllium is etched.

The etched beryllium is then placed in a bath containing, in each liter, 120 grams of sodium stannate, 7.5 grams of sodium hydroxide, grams of sodium acetate, and 0.5 gram of hydrogen peroxide. The beryllium, as a cathode, is plated at a current density of 0.15 ampere per square inch at from 60 to 90 C. for about 10 minutes. The tin plate is smooth, uniform and free of all pore holes.

There are, of course, many possible embodiments of the method of this invention. The beryllium metal composition may be cleaned before etching in ways other than by rendering it cathodic in a potassium hydroxide solution or by immersing it in acetone.

The etching step need not be carried out in a Pyrex or a stainless steel container, but may be carried out in any container which is not appreciably soluble in the electrolyte.

Aspointed out hereinbefore the anode need not be pure beryllium, but may be any beryllium metal composition containing a major proportion by weight of beryllium. The cathode may be nickel as in Example I or carbon as in Example II, or any metal which is not appreciably reactive in the electrolyte. The current density may be varied. from. 0.1 to 0.5 ampere per square inch "without affecting the efiiciency of the method.

The composition and concentration of the strong, monobasic oxygen-free acidv used in the electrolyte may be varied within wide limits. Other strong monobasic oxygen-free acids such as hydrobromic acid may be used in place of or along with the hydrochloric or hydrofluoric acid used in the examples. A small amount of strong monobasic oxygen-free acid is desirable because it causes the electrolytic solution to pit the surface somewhat and thus when the beryllium or beryllium metal composition is coated, the coating ismore adherent. On the other hand, if the concentration of the strong, monobasic oxygen-free acid is increased, the electrolyte attacks the surface exceptionally rapidly. As an example of a possible variation in concentration, from 1 to 10 cubic centimeters of hydrochloric acid per liter of electrolyte, that is, from 0.1 to 1 percent hydrochloric acid by volume, gives satisfactory results.

In like manner, the strong, polybasic inorganic oxygen-containing acid, which attacks the berylliu-m at a slow, steady rate, may also be varied in composition and concentration. Sulfuric acid or phosphoric acid may be used as the polybasic inorganic oxygencontaining acid. The concentration may be varied, for example, when concentrated phosphoric acid is used, between 250 to 700 cubic centimeters of the acid per liter of electrolyte, that is, from about 25 to '70 percent by volume. The etching step has the advantage of high current efiiciency. It also has other advantages such as control of the rate of cleaning over a wide range by simple current manipulation.

As noted hereinbefore, the etch may be improved by a second step which comprises treating the beryllium with an acid bath containing sulfate ions. The concentration of this bath may also be varied. For example, sulfate ions may be added continuously to maintain a predetermined concentration. It is, however, more convenient to add a quantity of ammonium sulfate which acts as a bufier. Satisfactory results are obtained when the ammonium sulfate is varied from 50 to 200 grams per liter and the sulfuric acid is varied from 25 to '75 cubic centimeters per liter.

After the beryllium metal composition is etched, it may be coated by the decomposition of compounds such as illustrated in Example I, it may be coated by metal spray, or it may be electroplated. It is of coursev possible to electroplate the composition with other metals than the tin used in, Example II. For example, the etched beryllium metal compositions may be plated with nickel, cadmium, or indium, or, for special uses, with silver or gold. It is also possible to electroplate with more than one metal, or to use a combination of, any of the plating methods. When beryllium which has been etched by the method of this invention is plated, a smooth, uniform, pore-free plate is usually obtained.

It is to be understood that when beryllium metal composition is stated. in the disclosure or in the appended claims, either pure beryllium, beryllium alloy, or beryllium metal compacts containing a major proportion by weight of beryllium are meant.

Because many embodiments of the invention are possible without departing from its spirit or scope, it is to be understood that it is not to be limited. except as indicated by the appended claims.

What is claimed is:

1. The method of treating compositions of beryllium prior to coating which comprises making the composition cathodic in a potassium hydroxide solution having a normality of about 1 and subjecting the composition while therein to a current density of about 0.5 ampere per square inch for about three minutes, removing the composition, making it anodic in a solution consisting essentially of from about 25 to 70 percent by volume of concentrated phosphoric acid, from 0.1 to 1 percent hydrochloric acid by volume and the remainder water and subjecting it while in the solution to a current density of from about 0.1 to about 0.5 ampere per square inch for a period of from above five to about ten minutes, removing the article, washing it in water, and dipping it in an aqueous solution consisting essentially of from about 50 to 200 grams per liter of ammonium sulphate and from about 25 to cubic centimeters per liter of concentrated sulphuric acid.

2. The method of treating compositions of beryllium prior to coating which comprises making the composition cathodic in a potassium hydroxide solution having a normality of about 1 and subjecting it. to. a current density of about 0.5 ampere per square inch for about three minutes, removing the composition, making it anodic in a solution consisting essentially of about 49 percent by volume of concentrated phosphoric acid, about 49 percent by volume of water and 0.9 percent by volume of hydrochloric acid and subjecting it to a current density of about 0.5 ampere per square inch for a period of about five minutes, removing the article, washing it in water, and dipping it in an aqueous solution consisting essentially of about 20grams of ammonium sulphate, 10 cubic centimeters of concentrated sulphuric acid and 200 cubic centimeters of water.

MORRIS KOLODN'EY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Chemical Abstracts, vol. 39 (1945), 5183; abstract of article by E. E. Halls in Metal Treatment,

' vol. 12, No. 42, pp. 71-85 (1945). 

1. THE METHOD OF TREATING COMPOSITIONS OF BERYLLIUM PRIOR TO COATING WHICH COMPRISES MAKING THE COMPOSITION CATHODIC IN A POTASSIUM HYDROXIDE SOLUTION HAVING A NORMALITY OF ABOUT 1 AND SUBJECTING THE COMPOSITION WHILE THEREIN TO A CURRENT DENSITY OF ABOUT 0.5 AMPERE PER SQUARE INCH FOR ABOUT THREE MINUTES, REMOVING THE COMPOSITION, MAKING IT ANODIC IN A SOLUTION CONSISTING ESSENTIALLY OF FROM ABOUT 25 TO 70 PERCENT BY VOLUME OF CONCENTRATED PHOSPHORIC ACID, FROM 0.1 TO 1 PERCENT HYDROCHLORIC ACID BY VOLUME AND THE REMAINDER WATER AND SUBJECTING IT WHILE IN THE SOLUTION TO A CURRENT DENSITY OF FROM ABOUT 0.1 TO ABOUT 0.5 AMPERE PER SQUARE INCH FOR A PERIOD OF FROM ABOVE FIVE TO ABOUT TEN MINUTES, REMOVING THE ARTICLE, WASHING IT IN WATER, AND DIPPING IT IN AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF FROM ABOUT 50 TO 200 GRAMS PER LITER OF AMMONIUM SULPHATE AND FROM ABOUT 25 TO 75 CUBIC CENTIMETERS PER LITER OF CONCENTRATED SULPHURIC ACID. 